1. Field of the Invention
The present invention relates to a memory control system and to a technique for controlling booting of a processor.
2. Description of the Related Art
Techniques for protection of data read by a processor include for example the techniques disclosed in Laid-open Japanese Patent Application No. 2001-109629, Laid-open Japanese Patent Application No. 2003-196097 and Japanese Patent Application No. 2004-13905.
Laid-open Japanese Patent Application No. 2001-109629 discloses the preparation of two boot programs that are used by a processor; if normal start-up is not achieved by reading one of these boot programs, the other boot program is read.
Laid-open Japanese Patent Application No. 2003-196097 discloses that, in addition to the instructions, the boot ROM stores the expected value of the checksum of the instructions, a DSP (digital signal processor) reads the instructions in the boot ROM and writes these into instruction memory and then performs a checksum, using the expected value of the checksum in the boot ROM, on the instructions that have thus been read into the instruction memory.
Laid-open Japanese Patent Application No. 2004-13905 discloses a technique relating to code protection in the boot program.
Typically, when a processor performs processing for start-up, first of all, initialization is conducted by resetting the register values of the processor. Next, the processor reads the boot program from memory such as ROM (hereinbelow referred to for convenience in description as “boot memory”), expands the boot program which has thus been read into local memory that is connected with the processor, and, in accordance with this boot program which has thus been expanded into the local memory, reads the OS (operating system) from the boot memory and expands it into the local memory. In this way, the processor is started up.
With this arrangement, there is a possibility that, if there is an error in the data code constituting the boot program or OS that is read by the processor and for example written to the registers, the processor may start up using this spurious data code, resulting in the processor hanging up (for example performing other processing than the processing which ought to be performed). The possibility of this is further increased in cases where for example an updated OS version is overwritten onto the boot memory and, due to for example some failure in overwriting, spurious data codes are written to the boot memory.